Water, moisture, odors, radon, organics, and various environmental pollutants or toxins in the form of liquids, gases, and particulates enter building structures through several entry mechanisms. These harmful and/or unpleasant substances may enter the structure by penetrating basement walls and slab materials through small pores, openings and cracks in the walls or slab or even by capillary action through a solid wall or slab to diffuse into the useable or living space of the structure.
There are many sources and environmental conditions permitting water and harmful and/or unpleasant substances to affect a structure, such as surface water, saturated ground water, high water table, outgassing, tunnels built by animals, clogged gutters, nearby construction, wet weather, springs, tree roots, exterior humidity condensing on cooler surfaces, as well as shrinking and swelling of the soil. There are several ways water and other substances may enter a basement or lower portion of a structure such as bleeding and sweating of the walls, entering through wall cracks and mortar joints, and entering over as well as under the footing, and through cracks in the floor. Water can collect at a buildings foundation causing moisture to enter the building through capillary action. Water can also cause structural damage. Standing water inside hollow cores in masonary block walls allows slack acid to form undermining the foundation by deteriorating the block walls.
Lesser amounts of water or moisture enter the structure causing the inhabitable space within the structure to have an unpleasant damp or musty odor. In addition to the previously stated sources, there are interior sources of moisture such as humidifiers, unvented clothes dryers, bathrooms, kitchens, and moisture in the concrete adding to the moisture inside the structure. Conditions compounding the build up of moisture in the structure are structures that are sealed tight for energy efficiency, tight fitting windows and doors, and other conditions that stagnate the air in the structure. Stagnant air can cause a build up of moisture as well as indoor pollutants, disease-causing toxins, infectious organisms, gases such as radon, odors, humidity, allergens, mold toxins, and pet dander, in a structure. Additionally, moisture in the basement or lower area of the structure can result in damage to the foundation and lower part of the structure and the formation of mold in building materials, carpets and furnishings. Molds have been found to produce objectionable odors, allergic reactions, and even illnesses and possibly compromise the immune system. Moisture can also attract spiders, silverfish, centipedes, and other such pests.
Pollutants known to enter basements and lower areas of a structure include radioactive radon gas and its progeny. These radionuclides emit the alpha radiation which can cause lung cancers. Other known pollutants to enter the structure include waste materials, lawn fertilizers, herbicides, pesticides, methane and other gases, natural organic content of the soil from decaying matter, bacteria, soil fungal propagules, funguses, and outgasses. These harmful and/or unpleasant substances enter a structure by several mechanisms. Sump pumps, floor drains, cracks, and service openings typically provide a path of direct entry into the lower portion of a structure.
Various systems have been employed in an attempt to reduce or prevent the entry of water, moisture, and pollutants into building structures. Dehumidifiers, aeronizers, and air filtration systems have had limited success in specific areas of a structure but have failed to completely mitigate the problems and require frequent maintenance, make noise, and take up floor space. Correcting basement concrete wall cracking and leakage is probably the most common and costly repair made to structures in an attempt to mitigate water and pollutant problems. These have included plugging cracks in foundation slabs and basement walls, and sealing and venting sump pumps and other such openings. However, these fixes alone have been found to only mitigate the water for a specific period of time and have limited or little effect on the moisture and pollutants entering the structure. With such an ad hoc preventative approach it is virtually impossible to permanently seal all cracks, and thus, the entry of soil pollutants or foundation water by this mechanism is not fully and permanently abated.
The natural stack effect of a structure has been used by drawing in cooler outside air through openings in the structure below the neutral pressure zone of the structure and exhausting the warmed inside air from an upper portion of the structure. This buoyancy-induced stack effect does not work when it is too hot outside. The air pressure of the basement area is generally at a lesser air pressure than that of the external soil air causing soil gases to be drawn into any openings such as basement or foundation cracks into the building structure.
Other systems have also been tried, but these have also been found to be problematic. These include exhausting a weeping tile to the outdoor air so as to depressurize around the slab wall interface so that any soil gases may escape to the atmosphere without entering the lower portion of the structure. However, this approach does not deal with water leakage and condensation problems and fails to mitigate indoor moisture or pollutants that have entered the structure. Additionally, weeping tile can become plugged and the layer of gravel may not allow free air movement to the exhaust. Further, since moisture and entrained gases can travel through the concrete by capillary action and mass diffusion, only partial mitigation is achieved.